Porous

Porous is a term used in materials science to describe solids that contain void spaces, or pores, within their structure. The porosity of a material is the fraction of its volume that is occupied by these voids. Pores can be connected (open porosity) or isolated (closed porosity). Open porosity allows fluids and gases to move through the material, while closed porosity does not.

Pore sizes are commonly classified as microporous (<2 nanometers), mesoporous (2–50 nanometers), and macroporous (>50 nanometers). The pore structure, including size distribution and connectivity, strongly influences transport properties such as permeability and diffusion.

Porous materials occur naturally (bones, wood, sponges, soils) and are engineered for a wide range of applications. They include ceramics, polymers, metals, and composites. High porosity and surface area make such materials useful for filtration and separation, catalysis, adsorption, and gas storage; their low density and insulating properties suit construction and thermal/acoustic insulation; porous scaffolds are used in tissue engineering and regenerative medicine; and porous rocks and sands act as reservoirs in oil and groundwater systems.

Characterization methods include Archimedes principle for porosity, helium pycnometry for skeletal density, mercury intrusion porosimetry for pore size distribution, and gas adsorption (BET) for surface area and pore volume.

Manufacturing methods to create porosity include foaming, leaching of porogens, sintering, etching, and additive manufacturing. The term porous thus describes a broad class of materials whose void structure governs how fluids, gases, heat, and electrons move through them.